.alpha.-Amylases (.alpha.-1,4-glucan-4-glucanohydrolases, EC 3.2.1.1) constitute a group of enzymes which catalyze hydrolysis of starch and other linear and branched 1,4-glucosidic oligo- and polysaccharides.
There is a very extensive body of patent and scientific literature relating to this industrially very important class of enzymes. A number of .alpha.-amylase such as Termamyl-like .alpha.-amylases variants are known from e.g. WO 90/11352, WO 95/10603, WO 95/26397, WO 96/23873 and WO 96/23874.
Among more recent disclosures relating to .alpha.-amylases, WO 96/23874 provides three-dimensional, X-ray crystal structural data for a Termamyl-like .alpha.-amylase which consists of the 300 N-terminal amino acid residues of the B. amyloliquefaciens .alpha.-amylase and amino acids 301-483 of the C-terminal end of the B. licheniformis .alpha.-amylase comprising the amino acid sequence (the latter being available commercially under the tradename Termamyl.TM.), and which is thus closely related to the industrially important Bacillus .alpha.-amylases (which in the present context are embraced within the meaning of the term "Termamyl-like .alpha.-amylases", and which include, inter alia, the B. licheniformis, B. amyloliquefaciens and B. stearothermophilus .alpha.-amylases). WO 96/23874 further describes methodology for designing, on the basis of an analysis of the structure of a parent Termamyl-like .alpha.-amylase, variants of the parent Termamyl-like .alpha.-amylase which exhibit altered properties relative to the parent.
WO 95/35382 (Gist Brocades B.V.) concerns amylolytic enzymes derived from B. licheniformis with improved properties allowing reduction of the Ca.sup.2+ concentration under application without a loss of performance of the enzyme. The amylolytic enzyme comprises one or more amino acid changes at positions selected from the group of 104, 128, 187, 188 of the B. licheniformis .alpha.-amylase sequence.
WO 96/23873 (Novo Nordisk) discloses Termamyl-like .alpha.-amylase variants which have increased thermostability obtained by pairwise deletion in the region R181*, G182*, T183* and G184* of the sequence shown in SEQ ID NO: 1 herein.